The Atlantic hurricane season is officially from 1 June to 30
November. There is nothing magical in these dates, and hurricanes
have occurred outside of these six months, but these dates were
selected to encompass over 97% of tropical activity. June 1st has
been the traditional start of the Atlantic hurricane season for
decades. However, the end date has been slowly shifted outward,
from October 31st to November 15th until its current date of
November 30th.

The Atlantic basin shows a very peaked season from August through October,
with 78% of the tropical storm days, 87% of the minor (Saffir-Simpson
Scale categories 1 and 2 - see Subject D1)
hurricane days, and 96% of the major (Saffir-Simpson categories
3, 4 and 5) hurricane days occurring then (Landsea (NHC)
1993). Maximum activity is in early to mid September. Once
in a few years there may be a tropical cyclone occurring "out
of season" - primarily in May or December. (For more detailed
information, see Subject G12 - "What is my
chance of having a tropical storm or hurricane strike by each
month?")

The Northeast Pacific basin has a broader peak with activity
beginning in late May or early June and going until late October
or early November with a peak in storminess in late August/early
September. NHC's official dates for this basin are from May 15th to
November 30th.

Paul Stanko (Guam WFO)

The Northwest Pacific basin has tropical cyclones occurring
all year round regularly. There is no official definition of
typhoon season for this reason. There is a distinct minimum in
February and the first half of March, and the main season
goes from July to November with a peak in late August/early September.

The North Indian basin has a double peak of activity in May and
November though tropical cyclones are seen from April to December. The
severe cyclonic storms (>33 m/s winds [76 mph]) occur almost
exclusively from April to June and late September to early December.

The Southwest Indian and Australian/Southeast Indian basins
have very similar annual cycles with tropical cyclones beginning
in late October/early November, reaching a double peak in
activity - one in mid-January and one in mid-February to early
March, and then ending in May. The Australian/Southeast Indian
basin February lull in activity is a bit more pronounced than
the Southwest Indian basin's lull.

The Australian/Southwest Pacific basin begin with tropical cyclone
activity in late October/early November, reaches a single peak in late
February/early March, and then fades out in early May.

Globally, September is the most active month and May is the least
active month. (Neumann 1993)